Device for producing water from ambient air

ABSTRACT

The invention concerns a device for producing water from ambient air comprising a heat pump with a cooling unit and a receiver for collecting the water that formed as condensed water vapour on a cooling surface of the cooling unit. In accordance with the invention the cooling surface is located in a closed space and a water vapour permeable membrane separates the ambient air and the closed space.

The invention concerns a device in accordance with the preamble of claim1. Such a device is known and in the known devices the ambient aircirculates around the cooling surface and the water vapour in theambient air condenses on the cooling surface. In the known devices, thecooling surface also cools the ambient air. This means that only part ofthe available cooling capacity is available for condensing the watervapour, which is a disadvantage. A further disadvantage is that theambient air contains dust particles that will mix with the condensedwater vapour and contaminate the water collected from the coolingsurface.

In order to overcome these disadvantages the device is in accordancewith claim 1. In this way, the ambient air does not enter the closedroom and is not exposed to the cooling surface, so that the coolingsurface cools only the water vapour and all water vapour that contactsthe cooling surface passes through the membrane that filters out alldust particles.

In accordance with an embodiment, the device is according to claim 2. Inthis way, the size of the closed space can be small as there is no needto locate the cooling unit inside the closed space. In addition, thismakes it easier to maintain a low pressure in the closed space.

In accordance with an embodiment, the device is according to claim 3. Inthis way, the dimensions of the closed space can be small and thecondensing of the water vapour can take place at a specific locationthat can be easy accessible.

In accordance with an embodiment, the device is according to claim 4. Inthis way, a simple heat pump is available.

In accordance with an embodiment, the device is according to claim 5.This reduces the heat transfer between the cooling surface and the wallsof the closed space, so that more cooling capacity is available forcondensing water vapour.

In accordance with an embodiment, the device is according to claim 6.This reduces heat transfer into the closed space, so that all coolingcapacity of the cooling unit is available for condensing water vapour.

In accordance with an embodiment, the device is according to claim 7. Inthis way, the membrane can withstand to the pressure differences overthe membrane easily.

In accordance with an embodiment, the device is according to claim 8. Inthis way, it is easy to replace the membrane.

In accordance with an embodiment, the device is according to claim 9.This prevents clogging of the openings in the membrane by fluid and themembrane remains permeable for water vapour.

In accordance with an embodiment, the device is according to claim 10.In this way, it is easy to clean the outside surfaces of the membraneand to remove the dust from the ambient air.

In accordance with an embodiment, the device is according to claim 11.In this way, the air around the membrane is refreshed continuously, sothat as much water vapour in the air as possible can pass the membrane.

In accordance with an embodiment, the device is according to claim 12.In this way, the excess heat of the heat exchanger creates the airflowover the membrane so that no additional equipment is necessary and noadditional costs arise.

In accordance with an embodiment, the device is according to claim 13.In this way the capacity of the heat exchanger and the membrane isincreased

In accordance with an embodiment, the device is according to claim 14.In this way, the available wind power or water power is used in the mostefficient way to obtain clean fresh water.

In accordance with an embodiment, the device is according to claim 15.This obtains a robust and compact installation that is quick and easy toerect.

In accordance with an embodiment, the device is according to claim 16.In this way, the available wind that drives the wind turbine circulatesair over the membrane and/or the heat exchanger as well, so that noadditional equipment is required.

The invention will be described hereafter with the aid of anillustrative embodiment and with reference to a drawing, in which:

FIG. 1 shows a diagram of an embodiment for producing water from ambientair,

FIG. 2 shows a schematic view of a wind turbine with the embodiment ofFIG. 1, and

FIG. 3 shows a section of a membrane assembly as used in embodiments ofFIGS. 1 and 2.

FIG. 1 shows a heat pump 2, which is indicated with an interrupted lineand which comprises a compressor 1, a condenser 6 and an evaporator 23,connected by piping 8. The evaporator 23 is located in a closed space 27that has an insulating wall 26. A canal 18 connects the closed space 27to the ambient air, membrane assemblies 10 close the opening of thecanal 18. The membrane assemblies 10 extend into an air duct 5, throughwhich ambient air flows in flow direction 4 so that the membranes of themembrane assemblies 10 are always surrounded by fresh ambient air.

The ambient air enters the air duct 5 through inlet opening 12 andpasses partitions 11, which remove water droplets from the air, thewater droplets assemble as water in a water receptacle 15. The air flowsupwards in flow direction 4 and passes over the membrane assemblies 10,flows through condenser 6 and out into the open air through outletopening 3. The condenser 6 heats the airflow, which will cause the airto rise upwards so that the air will flow in the flow direction 4. Ifnecessary a ventilator 7, indicated with interrupted lines in air duct5, will boost the airflow, which ensures an uninterrupted flow of freshair over the membrane assemblies 10 and through the condenser 6.

A drive unit 28 drives the compressor 1 of heat pump 2. The heat pump 2is designed such, that in operation heat is transported from the closedspace 27 to the condenser 6 and from the condenser 6 the heat disappearsinto the ambient air. The evaporator 23 is in the closed space 27 and acontrol system (not shown) of the heat pump 2 arranges that thetemperature of the evaporator 23 is below 20° C. or preferably below 10°C. but at least slightly above 0° C.

It will be clear to the skilled man that as long as there is water inthe closed space 27 the gas pressure of the water vapour in the closedspace 27 will be determined by the temperature of the water, as thewater will evaporate to water vapour. In most situations, thetemperature of the water will be equal to the temperature of theevaporator 23. The ambient air also contains water vapour with a gaspressure. The water vapour pressure in the ambient air depends on thetemperature of the air and the water saturation level in the ambientair.

The membrane assemblies 10 have membranes that separate the ambient airand the inside of the closed space 27. The membranes in the membraneassemblies 10 are permeable for water vapour and substantial impermeablefor other gases such as nitrogen and oxygen. This means that watervapour can enter into the closed space 27 if the water vapour pressurein the ambient air is higher than the water vapour pressure in theclosed space 27. The water vapour will flow through the membrane intothe closed space 27 and this flow of water vapour into the closed space27, will increase the pressure in this closed space 27. As soon as thepressure in the closed space 27 increases above the saturation pressurethat belongs to the temperature of the evaporator 23, the water vapourwill condense on the evaporator 23 and flow into a water receptacle 22.

The condensing water vapour generates heat that increases thetemperature of the evaporator 23 unless the cooling capacity of theevaporator 23 is sufficient. This means that the cooling capacity of theevaporator 23 limits the quantity of water that can be condensed. If thetemperature of the evaporator 23 rises, the pressure of the water vapourin the closed space 27 rises as well and due to the reduced pressuredifference on both sides of the membrane less water vapour will enterthe closed space 27 so that no additional measures are necessary. In thesituation that the water vapour pressure in the ambient air is low, theair is dry and/or cold, it is possible that insufficient water vapourenters the closed space 27 through the membrane. Then the quantity ofcondensing water reduces and there is less heat generated throughcondensing. This means that the temperature of the evaporator 23 lowers.In order to prevent freezing of the evaporator 23 the control systemmust then reduce the cooling capacity of the heat pump 2 or switch itoff.

A pump 20 will pump the condensed water through a condensed water drain19 into a tank 21, where it is available for further use. A vacuum pump24 removes the air from the closed space 27, so that there is a pressuredifference of approximately one atmosphere over the membrane assemblies10. If other gases than the water vapour leak through the membranes intothe closed space 27 the vacuum pump 24 will remove these. In situationswhere in the water level in the tank 21 is for instance 10 meters belowthe closed space 27, it is possible to connect the drain 19 without thepump 20 to the tank 21. It is possible then to maintain the near vacuumin the closed space 27 and to have an open connection with the tank 21,the water level in the drain 19 will then be approximately 10 metersabove the water level in the tank 21.

From the above it is clear that the difference in the pressure of thewater vapour on both sides of the membrane determines the quantity ofwater entering the closed space 27. The pressure difference whereby thewater vapour enters the closed space 27 only arises when the temperatureinside the closed space 27 is lower than the temperature of the ambientair. The pressure difference increases as the temperature differencebetween inside and outside the closed space 27 increases, and with thatthe collected quantity of water increases but can only arise if there issufficient water vapour pressure in the ambient air and the ambient airis not too dry. The heat pump creates the temperature difference betweenthe ambient air and the closed space 27.

The membrane assemblies 10 must be cleaned from time to time, dependingon the circumstances in the ambient air. Sprays heads 9 spray water onthe membranes of the membrane assemblies 10 and rinse their outersurfaces clean and free of dust. The rinsing water assembles in thewater receptacle 15 and drains away through drainpipe 17 to the drain16.

The disclosed embodiment has a heat pump 2, which comprises a compressor1, a condenser 6, and an evaporator 23, connected by piping 8 throughwhich refrigerant circulates. The compressor 1 compresses therefrigerant, which refrigerant condenses to a fluid in the condenser 6,thereby releasing heat, and which fluid evaporates in the evaporator 23to a gas, thereby cooling the inside of the closed space 27. It ispossible to use other types of heat pumps that cool the inside of theclosed space 27. For instance in a further embodiment instead ofcirculating refrigerant it is possible to circulate water and watervapour, whereby compressed water evaporates in the closed space 27, andthe compressor 1 compresses water vapour to water.

In another further embodiment of a heat pump an absorbent can be used,such as described hereafter. Also heat pumps with a carrier fluid/gassuch as NH3 are known. In the embodiment, the circulating fluid can bewater that evaporates in a evaporator in the cooling space 27. The watervapour flows through piping alternating to a first vessel and the secondvessel and an absorbent such as silica gel absorbs the water vapour.Solar heat heats the vessel that is not absorbing the water vapour,respectively the second vessel and alternating the first vessel, and theabsorbent dries because of the heating and the evaporating water vapourflows through piping to a heat exchanger where it condenses and wherebythe ambient air cools the heat exchanger.

It will be clear that combinations of the earlier described embodimentsfor cooling the inside of the closed space 27 are possible and withinthe scope of the invention. In a further embodiment, it is also possiblethat the evaporator 23 has cooling surfaces that are located inside theclosed space 27 or that the cooling surfaces form part of the wall ofthe closed space 27. In that situation, other parts of the evaporator 23can be outside the closed space 27. In a further embodiment, the closedspace 27 can include a pump that transports the water vapour from themembrane to the cooling surface.

A control system (not shown) controls the various parts of the describedinstallation, the control system has sensors for instance for measuringthe temperatures, water levels, and gas pressures.

FIG. 2 shows an embodiment of the water producing installation with awind turbine with a tower 31 supported on a foundation 35 via a bearing34. Support 33 keeps the tower 31 upright and wheels 32 mounted in aring of the support 33 make it possible that the tower 31 rotates arounda vertical axis, the wheels 32 are provided with a drive (not shown) forrotating the tower 31 with the blades 32 to the wind. On top of tower 31a nacelle 29 supports the blades 30 of the wind turbine, the compressor1 is in the nacelle 29 and the rotating blades 30 drive the compressor1.

The inlet opening 12 is at the side of the blades 30 in the lower partof the tower 31; the outlet opening 3 is at the opposite side of thetower 31 near the top of a tower 31. The air duct 5 connects the inletopening 12 and the outlet opening 3. The closed space 27 is locatedalongside the air duct 5 and the membrane assemblies 10 extend into theair duct 5 so that the upwards flowing air in the air duct 5 flows overthe membranes. The air duct 5 has spray heads 9 above the membraneassemblies 10 and the water receptacle 15 is below the membraneassemblies 10. The evaporator 23 is in the closed space 27 and thecondenser 6 is in the air duct 5 immediately above the spray heads 9. Ina further embodiment (not shown) the evaporator 23 can be in the airduct 5 near the inlet opening 12, so that the height of the air duct 5above the evaporator 23 forms a chimney in which the air heated in theevaporator 23 can rise and expand and so creates a strong upward airflow.

The water tank 21 is below the closed space 27 and is filled with thepump 20 (not shown). In a further embodiment (not shown), where theclosed space is higher in the tower 31 and the water tank 21 is near thebottom of the tower 31 and the water level in the water tank 21 is morethan 10 meters below the closed space 27, it is possible to drain theclosed space 27 without the use of a pump.

It will be clear to the skilled man that the wind turbine can bepositioned on different type of towers. For instance in an embodimentthe tower is stationary, and the nacelle rotates on top of the tower. Itis then possible that the closed space 27 is stationary or that itrotates with the nacelle.

For driving the various components of the installation shown in FIG. 2,which includes the control system, there is a power supply (not shown).The power supply can be external, for instance from the grid, or theblades 30 of the wind turbine can drive a generator (not shown) that isconnected to an accumulator and so makes power available for the variousequipments.

FIG. 3 shows an embodiment of the membrane assembly 10. A hollow fibre38 of the suitable semi permeable material with a length ofapproximately 1 m and a diameter of 3 mm is bent for instance in aU-shaped form and both ends of the fibre 38 are embedded in the flange36 by moulding them in a resin. The openings 37 of the hollow fibre 38end at one side of the flange 36, which is the side of the inner room ofthe closed space 37. One flange 36 can contain several hundred fibres 38so that a membrane assembly 10 comprising one flange 36 will have amembrane surface of several square metres. If necessary, the flange 36will have a support structure for supporting the U-shaped hollow fibres38. The membrane assemblies 10 are mounted with their flanges 36 in thewall of the closed space 27 in such a way that used membrane assemblies10 can rapidly be replaced by new ones.

1. Device for producing water from ambient air comprising a heat pump(2) with a cooling unit (23) and a receiver (22) for collecting thewater that formed as condensed water vapour on a cooling surface of thecooling unit, characterized in that the cooling surface (23) is locatedin a closed space (27) and a water vapour permeable membrane (38)separates the ambient air and the closed space.
 2. Device in accordancewith claim 1 wherein the cooling surface comprises at least part of awall of the closed space (27).
 3. Device in accordance with claim 1 or 2wherein the closed space includes a pump for transporting water vapourto the cooling surface.
 4. Device in accordance with claim 1, whereinthe heat pump (2) comprises a compressor (1), a condenser (6) and anevaporator (23), the evaporator forming the cooling unit and thecompressor, condenser and evaporator being connected by piping (8). 5.Device in accordance with claim 1, wherein the closed space (27) isconnected to a vacuum pump (24) for removing air and/or other gassesfrom the closed space.
 6. Device in accordance with claim 1, wherein theclosed space (27) has insulating walls (26).
 7. Device in accordancewith claim 1, wherein the membrane comprises hollow fibres (38) and theclosed space (27) connects to the inside (37) of the hollow fibres. 8.Device in accordance with claim 1, wherein the membrane (38) comprises anumber of units mounted in exchangeable cassettes (10).
 9. Device inaccordance with claim 1, wherein a canal (55) guides an airflow (4) overthe membrane (10) and wherein the canal comprises partitions (11) toblock fluid particles.
 10. Device in accordance with claim 1, wherein arinsing system (9, 15) cleans the ambient-air side of the membrane (10).11. Device in accordance with claim 1, wherein a ventilator (7) providesairflow over the membrane (10).
 12. Device in accordance with claim 1,wherein the condenser (6) includes a heat exchanger that generatesairflow over the membrane (10).
 13. Device in accordance with claim 1,wherein the condenser (6) includes a heat exchanger and a ventilator (7)generates airflow over the membrane (10) and the heat exchanger. 14.Device in accordance with claim 1, wherein a turbine, such as a windturbine (30) or a water turbine, drives the compressor (1).
 15. Devicein accordance with claim 1, wherein the heat pump (2) is mounted in thetower (31) of a wind turbine (30).
 16. Device in accordance with claim15 wherein the tower (31) has an inlet opening (12) for the airflowalong the membrane (10) and/or a heat exchanger and wherein the inletopening rotates with the direction of the wind.